The purpose of the present study is to determine the effects of phencyclidine and the related anesthetic agent ketamine on synaptic transmission in the central nervous system using three approaches: The first one consists in studying the effects of intravenous or iontophoretic applications of PCP and ketamine on the single-unit activity of identified neurones in the CNS and on their responsiveness to the local application of a variety of neurotransmitters. This type of experiments allows to determine whether PCP or ketamine antagonizes or potentiates the action of any given neurotransmitter or classes of neurotransmitters. The second approach consists in studying the effect of i.v. or iontophoretically applied PCP and ketamine on phasic neuronal responses (field potentials or single-unit activity) evoked by the electrical stimulation of afferent pathways. Various aspects of the hippocampal circuitry are being examined in this respect. The third approach consists in determining the effects of the drugs in an "in vitro" model (hippocampal slice) to relate the "in vivo" effects to intracellular events.